1. Field of the Invention
This invention relates to a keyboard interface circuit, and more particularly a test system for testing such a circuit.
2. Prior Art
As shown in FIG. 3, a conventional keyboard interface circuit 2 comprises an input shift register 8 which stores data signals from a keyboard 4 and outputs them to a microprocessor 6 after shifting the signals responsive clock signals from the keyboard 4, and an output shift register 10 which stores data signals to be supplied from the microprocessor 6 to the keyboard 4 and outputs them to the keyboard 4 according to the clock signals from the keyboard 4. Existence of trouble in the keyboard 4 or the interface circuit 2 is determined by observing whether or not predetermined data entered from the keyboard 4 reach the microprocessor 6.
The above-described conventional testing method has a shortcoming in that, if the entered data from the keyboard 4 fails to reach the microprocessor 6, it is impossible to determine whether the trouble is in the interface circuit 2 or the keyboard 4.